How can it be a surprise that you have a narrow pelvis? It's a bone. You can see it on an x-ray. You can feel it. This sounds like a fact determinable by means other than "will an x cm baby skull fit through it? no? guess it's narrower than x cm!"
(via the MeFi thread on Gawande's article, with extra added OMG from Deadspin and Rural Doctoring)